Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Normal reaction

  1. Feb 20, 2010 #1
    The weight (mg) is balanced by the normal reaction acting on the body.
    But What is the reason for this force(normal reaction)?
  2. jcsd
  3. Feb 20, 2010 #2
    The nature of the normal reaction force is electromagnetic repulsion.
    The electrons on the surfaces repel each other, hence giving rise to the normal reaction force. In the absence of this force, the body, due to gravity, will fall through the object originally 'supporting' it.
  4. Feb 20, 2010 #3
    Could you explain more about the electromagnetic repulsion?
    Actually i didn't get the concept of charge.what is charge?Why does an electron possess negative charge and proton possess positive charge?Is that a convention?
  5. Feb 20, 2010 #4
    Basically its just electronic repulsion between the electrons, which carry the same charge.

    Charge is a certain property found to exist in matter. It gives rise to and interacts with the electromagnetic force. There are two types of charges which we denote as positive and negative. Electrons and protons possess opposite charges. Yes, it is conventional that we give the proton the positive charge and the electron the negative charge.
  6. Feb 21, 2010 #5
    Then how did we measure the charge on the electron as -1.6*10^(-19) ?
  7. Feb 21, 2010 #6
    This goes back to the old days before electrons were known to exist. Prior to that, electricity was already a known and studied phenomenon. Current was then taken to be the flow of positive charges. This unfortunately left no choice but to relegate the electron to possessing a negative charge - it is actually electrons flowing in the opposite direction that constitute a positive current/voltage.
  8. Feb 22, 2010 #7
  9. Feb 22, 2010 #8

    This course, of half hour lectures, will answer your questions on how we measure the charge of the electron (and how it was done), what magnetic repulsion is and about a billion more questions you wouldn't even think to ask. Life-changing experience.

    Btw, the normal force is a consequence of the interaction of two bodies caused by an external force. In other words, gravity pulls you down as you sit on your chair & if the chair/ground wasn't there you'd keep falling down until you hit the center of the earth. The normal force is an equal but opposite force. It's interesting when you do free-body diagrams of inclined planes etc... to see how this stuff changes and how it's all calculatable and understandable.
    Why you're repelled by the ground/chair etc... is due to magnetice interactions as stated above.
  10. Mar 2, 2010 #9
    Why like charges repel and unlike charges attract each other ?
  11. Mar 2, 2010 #10

    I think this is a step in the right direction to understanding the question you're asking.
    Last edited by a moderator: Sep 25, 2014
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook